Manufacturing method, golf club head, and design method

ABSTRACT

The present invention relates to a method of manufacturing a wood type golf club head including a face portion, a crown portion, and a sole portion. The method includes a setting step of setting a surface roughness of the face portion and a step of forming the face portion based on the surface roughness set in the setting step. In the setting step, the larger a moment of inertia of the golf club head is, the larger the surface roughness outside an impact area of the face portion is set, and the smaller the moment of inertia is, the smaller the surface roughness outside the impact area of the face portion is set.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wood type golf club head.

Description of the Related Art

In a golf club head having a relatively large loft angle, the larger thesurface roughness of the face portion is, the larger the spin amount ofa shot tends to be. However, in a golf club head having a relativelysmall loft angle (for example, 20° or less), the larger the surfaceroughness of the face is, the smaller the spin amount of a shot tends tobe. Japanese Patent Laid-Open No. 2008-79969 and 2004-222905 proposegolf club heads with a focus on this point.

In a golf club head, generally, the position of a hit on the faceportion may degrade the carry or spin amount of a shot. To improve this,each of Japanese Patent Laid-Open No. 2004-222905, 5-237206, and62-144674, Japanese Utility Model Laid-Open No. 3-16963, U.S. PatentApplication Publication No. 2012/0052980, and U.S. Pat. No. 6,309,310discloses a golf club head that changes the specifications of thesurface roughness or grooves depending on a portion on the face portion.

In a wood type golf club head, since the loft angle is relatively small,the larger the surface roughness of the face portion is, the smaller thespin amount of a shot tends to be. When a focus is placed only ondistance performance, increasing the surface roughness of the faceportion is advantageous. However, if the spin amount of a shot is small,and it is difficult for the golfer to intentionally bend the shot to theleft or right. This is disadvantageous from the viewpoint of shotcontrol.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wood type golfclub head including a face portion with a surface roughness suitable forthe specifications of the golf club head.

According to an aspect of the present invention it is provided a methodof manufacturing a wood type golf club head including a face portion, acrown portion, and a sole portion, comprising: a setting step of settinga surface roughness of the face portion; and a step of forming the faceportion based on the surface roughness set in the setting step, whereinin the setting step, the larger a moment of inertia of the golf clubhead is, the larger the surface roughness outside an impact area of theface portion is set, and the smaller the moment of inertia is, thesmaller the surface roughness outside the impact area of the faceportion is set.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a golf club head according to anembodiment of the present invention;

FIG. 1B is a front view showing the golf club head in FIG. 1A viewedfrom a face side;

FIG. 2A is a sectional view taken along a line I-I in FIG. 1B;

FIG. 2B is a sectional view taken along a line II-II in FIG. 1B;

FIGS. 3A and 3B are explanatory views of a face center and the like;

FIG. 4A is a flowchart showing an example of a method of manufacturingthe golf club head shown in FIG. 1A;

FIGS. 4B to 4E are views showing examples of the relationship between asurface roughness and a moment of inertia;

FIG. 5A is an explanatory view of an example of a shallow groove formingmethod;

FIG. 5B is a view showing another example of the arrangement of a faceportion;

FIGS. 6A to 6E are explanatory views of another example of shallowgrooves;

FIG. 7A is an explanatory view of a bulge; and

FIG. 7B is a view showing an example of the relationship between a bulgeand a moment of inertia.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIG. 1A is a perspective view of a golf club head 10 according to anembodiment of the present invention. FIG. 1B is a front view showing thegolf club head 10 viewed from the side of a face portion 11.

The golf club head 10 forms a hollow member. Its peripheral walls formthe face portion 11, a crown portion 12, a sole portion 13, and a sideportion 14. The surface of the face portion 11 forms a face (strikingface). A bulge and a roll are formed on the face. The crown portion 12forms the upper portion of the golf club head 10. The sole portion 13forms the bottom portion of the golf club head 10. The side portion 14forms the portion between the sole portion 13 and the crown portion 12.The golf club head 10 also includes a hosel portion 15 to which a shaftis attached.

An arrow d1 in FIG. 1A indicates a face-back direction, and an arrow d2indicates a toe-heel direction. An arrow d3 in FIG. 1B indicates thevertical direction of the face portion 11. The face-back direction isnormally a target line direction (the target direction of a shot). Thetoe-heel direction can be defined as, for example, a direction in whichthe toe-side end and the heel-side end of the sole portion 13 areconnected or a direction perpendicular to the face-back direction. Thevertical direction of the face portion 11 is defined based on the golfclub head grounded in accordance with a predetermined lie angle. In thisembodiment, the vertical direction is the direction of sole portion13−crown portion 12. Note that the lie angle is an angle θ1 made by ashaft axis line L1 and the ground surface, as shown in FIG. 1B.

The golf club head 10 is a golf club head for a driver. However, thepresent invention is applicable to wood type golf club heads including afairway wood other than drivers. The present invention is particularlysuitable for a golf club head having a loft angle of 20° or less. Thisembodiment assumes a golf club head having a loft angle of 20° or less.

The golf club head 10 can be made of a metal material. Examples of themetal material are a titanium-based metal (for example, titanium alloy6Al-4V-Ti), stainless steel, and a copper alloy such as berylliumcopper.

The golf club head 10 can be assembled by joining a plurality of parts.For example, the golf club head 10 can be formed from a main body memberand a face member. The main body member forms the crown portion 12, thesole portion 13, the side portion 14, and a peripheral portion of theface portion 11. An opening is formed at part of the portioncorresponding to the face portion 11. The face member is joined to theopening of the main body member.

A plurality of shallow grooves G1 to G3 (to be generically referred toas shallow grooves G) are formed in the surface of the face portion 11.The plurality of shallow grooves G will be described with reference toFIGS. 2A and 2B in addition to FIGS. 1A and 1B. FIG. 2A is a sectionalview taken along a line I-I in FIG. 1B. FIG. 2B is a sectional viewtaken along a line II-II in FIG. 1B. The line I-I and the line II-II arelines in the direction d3.

The plurality of shallow grooves G are arrayed in the vertical direction(direction d3) of the face portion 11. In this embodiment, the shallowgrooves G are straight grooves extending in the toe-heel direction andare parallel to each other. The shallow grooves G are formed so as to belevel when the golf club head 10 is grounded toward the targetdirection. In this embodiment, each shallow groove G need not always bea straight continuous groove and may break halfway.

In this embodiment, the plurality of shallow grooves G1 are formed in animpact area IA. The plurality of shallow grooves G2 are formed in atoe-side area TA out of areas other than the impact area IA, and theplurality of shallow grooves G3 are formed in a heel-side area HA out ofareas other than the impact area IA. A structure without the shallowgrooves in the impact area IA can also be employed.

In a driving club or a fairway wood, the impact area IA is a band-shapedportion passing through the center of the club face and having a widthof 1.68 inches (42.67 mm) under the rules (R & A rules). A supplementarydescription of the impact area IA will be made here with reference toFIGS. 3A and 3B as well.

Referring to FIGS. 3A and 3B, a plane S1 is a virtual vertical planethat passes through a geometric center FC of the face portion 11 and isperpendicular to the ground surface and the toe-heel direction when thegolf club head 10 is grounded at the predetermined lie angle θ1 and apredetermined loft angle θ2. As shown in FIG. 1B, the impact area IA isa band-shaped portion having a width of 1.68 inches (42.67 mm) withrespect to the intersection between the plane S1 and the face portion 11as the center.

Referring to FIGS. 1A, 1B, 2A, and 2B, the surface roughness of the faceportion 11 can be adjusted by the specifications, for example, thepitch, width, and depth of the plurality of shallow grooves. In thisembodiment, the specifications (here, for example, only the pitch) ofthe shallow grooves G are changed between the impact area IA and theareas TA and HA other than the impact area IA. However, thespecifications of the shallow grooves G may be the same between theimpact area IA and the areas TA and HA other than the impact area IA.

All or some of the specifications of the shallow grooves G may bechanged between the toe-side area TA and the heel-side area HA. In thisembodiment, however, the specifications of the shallow grooves G are thesame in both areas. Hence, in the following explanation, a descriptionconcerning the shallow grooves G2 in the toe-side area TA also appliesto the shallow grooves G3 in the heel-side area HA, unless otherwisespecified.

A depth D1 of each shallow groove G1 and a depth D2 of each shallowgroove G2 are less than, for example, 0.025 mm. If the depth is lessthan 0.025 mm, the shallow grooves G are handled not as so-called scorelines but as elements (for example, elements by milling) that roughenthe face under the rules (R & A rules) of golf club heads. The shallowgrooves G are formed to adjust the surface roughness of the face portion11. Hence, the depths D1 and D2 can be 0.005 mm or more. A width W1 ofeach shallow groove G1 and a width W2 of each shallow groove G2 canrange, for example, from 0.1 mm (inclusive) to 0.3 mm (inclusive). Notethat the widths W1 and W2 are the widths of the shallow grooves G in thevertical direction (the direction d3 or the planar direction of the faceportion 11).

In the examples shown in FIGS. 2A and 2B, the cross section of eachshallow groove G has an elliptic arc outline. However, the outline shapeof the cross section of each shallow groove G is not limited to this,and various outline shapes such as an arc shape, triangular shape,rectangular shape, and trapezoidal shape can be employed.

In this embodiment, the plurality of shallow grooves G are formed at anequal pitch. However, the pitch may change depending on a part. In thisembodiment, the pitch between adjacent shallow grooves G1 is P1, and thepitch between adjacent shallow grooves G2 is P2. A relationship P2<P1holds. That is, the surface roughness of the impact area IA is madesmaller (smoothened) at least in the direction d3 as compared to thesurface roughness in the areas TA and HA other than the impact area IA.The reason for this is as follows.

The golf club head 10 according to this embodiment is assumed to be agolf club head having a loft angle of 20° or less. The larger thesurface roughness of the face portion 11 is, the smaller the back spinamount tends to be, and the longer the carry of a shot tends to be. Onthe other hand, in a case in which the surface roughness of the faceportion 11 is uniform, if a hit exists outside the impact area IA, thecarry tends to deteriorate as compared to a case in which a hit existsin the impact area IA. With the relationship P2<P1, the back spin amountis made relatively large if a hit exists in the impact area IA, or theback spin amount is made relatively small if a hit exists outside theimpact area IA. This can decrease the difference in the carry caused bythe difference in a hit and implement more stable distance performance.

The surface roughness of the areas TA and HA other than the impact areaIA will be described next. In this embodiment, the surface roughness ofthe areas TA and HA other than the impact area IA is set in accordancewith the moment of inertia of the golf club head 10. More specifically,the larger the moment of inertia of the golf club head 10 is, the larger(rougher) the surface roughness of the areas TA and HA is set to be. Thesmaller the moment of inertia is, the smaller (smoother) the surfaceroughness of the areas TA and HA is set to be. The reason for this is asfollows.

In a case in which the moment of inertia of the golf club head 10 isrelatively large, if a ball strikes outside the impact area IA, aso-called gear effect becomes relatively weak. Not much of spin is givento a shot, and little bending of the trajectory of the shot to the leftor right occurs. In other words, the design intent for making the momentof inertia relatively large includes emphasizing distance performancewhile suppressing bending of the shot to the left or right. Hence, thelarger the moment of inertia of the golf club head 10 is, the larger thesurface roughness of the areas TA and HA is set. This can decrease thedifference in the carry caused by the difference in a hit and implementmore stable distance performance.

On the other hand, in a case in which the moment of inertia of the golfclub head 10 is relatively small, if a ball strikes outside the impactarea IA, a so-called gear effect becomes relatively strong. The spinamount is easily given to a shot, and bending of the shot to the left orright readily occurs. In other words, the design intent for making themoment of inertia relatively small includes allowing a golfer to easilybend a shot to the left or right, that is, emphasizing shot controlperformance. Hence, the smaller the moment of inertia of the golf clubhead 10 is, the smaller the surface roughness of the areas TA and HA isset. This can increase the spin amount of a shot and implementimprovement of shot control performance.

In this way, according to this embodiment, it is possible to provide awood type golf club head including a face portion with a surfaceroughness suitable for the specification (in particular, the moment ofinertia) of the golf club head.

FIG. 4A shows an example of a method of manufacturing the golf club head10, and particularly, steps concerning adjustment of the surfaceroughness of the areas TA and HA. In step S1, the moment of inertia ofthe golf club head 10 is referred to. The moment of inertia of the golfclub head 10 can be a design value or a measured value. The measuredvalue may be the measured value of the moment of inertia of the golfclub head 10 before the shallow grooves G are formed.

In step S2, the surface roughness of the face portion 11 is set. Detailswill be described later. In step S3, the face portion 11 is formed basedon the set surface roughness. Details will be described later.

Setting of the surface roughness of the face portion 11 in step S2 willbe described. First, the surface roughness of the areas TA and HA otherthan the impact area IA is set. As already described, the surfaceroughness of the areas TA and HA other than the impact area IA is set inaccordance with the moment of inertia of the golf club head 10. As anexample, the correlation between the moment of inertia and the surfaceroughness of the areas TA and HA is decided in advance by experimentsand the like and saved as data, as shown in FIG. 4B.

In the example of FIG. 4B, the moment of inertia and the surfaceroughness of the areas TA and HA have a linear relationship. The largerthe moment of inertia is, the larger the surface roughness is. Thesmaller the moment of inertia is, the smaller the surface roughness is.

As another example of the correlation, in the example shown in FIG. 4C(a line C1 or a line C2), the moment of inertia and the surfaceroughness of the areas TA and HA have a nonlinear relationship. In thiscase as well, the larger the moment of inertia is, the larger thesurface roughness is. The smaller the moment of inertia is, the smallerthe surface roughness is. When the line C1 is compared with the line C2,the line C1 exhibits a characteristic that increases the surfaceroughness as a whole.

As still another example of the correlation, in the example shown inFIG. 4D, the surface roughness is set for each range of the moment ofinertia. The contents of the example shown in FIG. 4D are as follows.

moment of inertia: smaller than m1, surface roughness: R1

moment of inertia: from m1 (inclusive) to m2 (exclusive), surfaceroughness: R2

moment of inertia: from m2 (inclusive) to m3 (exclusive), surfaceroughness: R3

moment of inertia: m3 or more, surface roughness: R4

In this example as well, the larger the moment of inertia is, the largerthe surface roughness is, and the smaller the moment of inertia is, thesmaller the surface roughness is.

As yet another example of the correlation, in the example shown in FIG.4E, the range of the surface roughness is set for each range of themoment of inertia. The designer sets the surface roughness within therange of the surface roughness corresponding to a moment of inertia. Thecontents of the example shown in FIG. 4E are as follows.

moment of inertia: smaller than m1, surface roughness: smaller than R1

moment of inertia: from m1 (inclusive) to m2 (exclusive), surfaceroughness: from R1 (inclusive) to R2 (exclusive)

moment of inertia: from m2 (inclusive) to m3 (exclusive), surfaceroughness: from R2 (inclusive) to R3 (exclusive)

moment of inertia: m3 or more, surface roughness: from R3 (inclusive) toR4 (exclusive)

In this example as well, the larger the moment of inertia is, the largerthe surface roughness is, and the smaller the moment of inertia is, thesmaller the surface roughness is.

The surface roughness of the areas TA and HA can be set within the rangeof, for example, 2.0 μm (inclusive) to 8.0 μm (inclusive) as anarithmetic mean roughness Ra. In addition, the surface roughness of theareas TA and HA can be set within the range of 2.0 μm (inclusive) to 6.0μm (inclusive) at minimum or within the range of 4.0 μm (inclusive) to8.0 μm (inclusive) at maximum. The moment of inertia of the golf clubhead 10 can fall within the range of 2000 g·cm² (inclusive) to 6000g·cm² (inclusive). The arithmetic mean roughness Ra can be thearithmetic mean roughness Ra when the average line is set in thedirection d3.

The surface roughness of the areas TA and HA is thus set on design. Inthis embodiment, the areas TA and HA have the same surface roughness butmay have different surface roughnesses.

Setting of the surface roughness of the impact area IA will be describednext. The surface roughness of the impact area IA can be set within therange of, for example, 1.0 μm (inclusive) to 4.0 μm (inclusive) as thearithmetic mean roughness Ra. When the surface roughness of the impactarea IA is made smaller than the surface roughness of the areas TA andHA, the difference in the carry caused by the difference in a hit can bemade small, and more stable distance performance can be implemented.

The surface roughness of the face portion 11 is thus set. In thisembodiment, the surface roughness of the face portion 11 is controlledby the shallow grooves G. Hence, the specifications of the shallowgrooves G to implement the set surface roughness are decided, and theprocess advances to step S3.

In step S3, the shallow grooves G are formed in the face portion 11. Asthe method of forming the shallow grooves G, machining, laser machining,chemical milling, etching, and press working are usable. Laser machiningis preferably used. As a procedure of processing, for example, the golfclub head 10 formed as a hollow member is fixed in a numericallycontrolled processing apparatus, thereby forming the shallow grooves Gin the face portion 11. FIG. 5A shows an example. In the example of FIG.5A, the golf club head 10 is fixed in a processing apparatus via a jig(not shown). A laser light irradiation device 100 is arranged facing theface portion 11. The irradiation device 100 moves while irradiating theface portion 11 with laser light, thereby forming the shallow grooves G.

As another procedure of processing, when assembling the golf club head10 by joining a plurality of parts, a flat face member is fixed in anumerically controlled processing apparatus, and the shallow grooves Gare formed. When formation of the shallow grooves G is completed, theface member is bent to form a bulge and a roll. After that, the facemember is joined to the opening of the main body member. In thisprocedure, since the face member is flat in the step of forming theshallow grooves G, the shallow grooves G can be formed more accurately.

In this embodiment, the surface roughness of the face portion 11 iscontrolled by the shallow grooves G. However, the shallow grooves G neednot always be used. For example, the surface roughness of the faceportion 11 may be adjusted by a process such as sand blast or shotpeening.

Second Embodiment

Score lines can be formed in a face portion 11 in addition to shallowgrooves G. FIG. 5B shows an example. In the example of FIG. 5B, scorelines 20 are formed in areas TA and HA other than an impact area IA. Thescore lines 20 are straight grooves extending in the toe-heel directionand are formed in parallel to each other.

The score lines 20 may be formed in the impact area IA as well. Astructure without the score lines 20 in the areas TA and HA other thanthe impact area IA can also be employed.

Third Embodiment

In the first embodiment, the shallow grooves G have been explained asstraight grooves. However, shallow grooves G may be grooves havinganother shape. FIGS. 6A to 6D show examples. FIGS. 6A and 6B showexamples of the shallow grooves G having wavy shapes. FIG. 6A shows acase in which the shallow grooves G are formed into a triangular waveshape, and FIG. 6B shows a case in which the shallow grooves G areformed into a sine wave shape. FIG. 6C shows an example in which theshallow grooves G are grooves having an arc shape. FIG. 6D shows anexample in which shallow grooves Ga having a triangular wave shape andshallow grooves Gb having a sine wave shape are repetitively formed. Asin this example, the shallow grooves G may be formed by periodicallyforming grooves having different shapes.

In the first embodiment, the shallow grooves G are formed so as to belevel when the golf club head 10 is grounded toward the targetdirection. However, the shallow grooves G need not be level. FIG. 6Eshows an example. FIG. 6E shows the shape of each shallow groove G whenthe golf club head 10 is grounded toward the target direction. Theshallow grooves G tilt from a level state.

Fourth Embodiment

In the first embodiment, the surface roughness of the areas TA and HAother than the impact area IA is set in accordance with the moment ofinertia of the golf club head 10. However, the surface roughness may beset in accordance with the bulge of a face portion 11. FIG. 7A is anexplanatory view of a bulge, which is the radius of curvature of thecurved surface (see an arrow) of the face portion 11 in a direction d2.

In this embodiment, the larger (flatter) the bulge of the face portion11 of a golf club head 10 is, the larger the surface roughness of areasTA and HA is set. The smaller (rounder) the bulge of the face portion 11is, the smaller the surface roughness of the areas TA and HA is set. Thereason for this is as follows.

In general, in a case in which the bulge of the face portion 11 of thegolf club head 10 is relatively large, if a ball strikes outside animpact area IA, the launch angle to the left or right becomes relativelysmall. In other words, the design intent for making the bulge relativelylarge includes emphasizing distance performance while suppressingbending of the shot to the left or right. Hence, the larger the bulge ofthe face portion 11 is relatively, the larger the surface roughness ofthe areas TA and HA is set. This can decrease the spin amount of a shotand make it such that the shot tends not to bend to the left or right.

Conversely, in a case in which the bulge of the face portion 11 of thegolf club head 10 is relatively small, if a ball strikes outside theimpact area IA, the launch angle to the left or right becomes relativelylarge. For this reason, it is preferable to easily give a spin amount toa shot and return the shot in the target direction by spin. In otherwords, the design intent for making the bulge relatively small includesallowing a golfer to intentionally bend a shot to the left or right,that is, emphasizing shot control performance. Hence, the smaller thebulge of the face portion 11 is relatively, the smaller the surfaceroughness of the areas TA and HA is set. This can increase the spinamount of a shot and make it easy to return the shot in the targetdirection.

In this way, according to this embodiment, it is possible to provide awood type golf club head including a face portion with a surfaceroughness suitable for the specification (in particular, the bulge) ofthe golf club head.

In this embodiment, as for setting of the surface roughness of the areasTA and HA in step S2, the correlation between the bulge and the surfaceroughness of the areas TA and HA is decided in advance by experimentsand the like and saved as data, as in the first embodiment. FIG. 7Bshows an example. The bulge and the surface roughness of the areas TAand HA have a linear relationship. The larger the bulge is, the largerthe surface roughness is. The smaller the bulge is, the smaller thesurface roughness is. In addition to the example of FIG. 7B, theexamples shown in FIGS. 4C to 4E are also applicable.

Note that the bulge of the face portion 11 may fall within the range of200 mm (inclusive) to 600 mm (inclusive), and the surface roughness ofthe areas TA and HA may fall within the range of 2.0 μm (inclusive) to8.0 μm (inclusive) as an arithmetic mean roughness Ra.

Fifth Embodiment

The methods of setting the surface roughness of the areas TA and HAaccording to the first and fourth embodiments are applicable to design aplurality of golf club heads.

For example, when designing a driver and a fairway wood, the head of thedriver relatively has a large moment of inertia, and the head of thefairway wood relatively has a small moment of inertia. Hence, thesurface roughness of areas TA and HA in each golf club head can be setsuch that the surface roughness of the areas TA and HA in the head ofthe driver becomes larger than in the head of the fairway wood, andconversely, the surface roughness of the areas TA and HA in the head ofthe fairway wood becomes smaller than in the head of the driver.

As another example, when designing a plurality of types of drivers, forexample, the head of a driver for skilled players may relatively have asmall moment of inertia, and the head of a driver for beginners mayrelatively have a large moment of inertia. Hence, the surface roughnessof areas TA and HA in each golf club head can be set such that thesurface roughness of the areas TA and HA in the head of the driver forbeginners becomes larger than in the head of the driver for skilledplayers, and conversely, the surface roughness of the areas TA and HA inthe head of the driver for skilled players becomes smaller than in thehead of the driver for beginners.

Similarly, if the bulge changes between a plurality of types of drivers,the surface roughness of areas TA and HA in each golf club head can beset such that the surface roughness of the areas TA and HA in the headof the driver having a relatively large bulge becomes larger than in thehead of the driver having a relatively small bulge, and conversely, thesurface roughness of the areas TA and HA in the head of the driverhaving a relatively small bulge becomes smaller than in the head havinga relatively large bulge.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-112389, filed Jun. 2, 2015 which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A method of manufacturing a wood type golf clubhead including a face portion, a crown portion, and a sole portion,comprising: a setting step of setting a surface roughness of the faceportion; and a step of forming the face portion based on the surfaceroughness set in the setting step, wherein in the setting step, thelarger a moment of inertia of the golf club head is, the larger thesurface roughness outside an impact area of the face portion is set, andthe smaller the moment of inertia is, the smaller the surface roughnessoutside the impact area of the face portion is set.
 2. A method ofmanufacturing a wood type golf club head including a face portion, acrown portion, and a sole portion, comprising: a setting step of settinga surface roughness of the face portion; and a step of forming the faceportion based on the surface roughness set in the setting step, whereinin the setting step, the larger a bulge is, the larger the surfaceroughness outside an impact area of the face portion is set, and thesmaller the bulge is, the smaller the surface roughness outside theimpact area of the face portion is set.
 3. The method according to claim1, wherein in the setting step, the surface roughness of the impact areaof the face portion is made smaller than the surface roughness outsidethe impact area of the face portion.
 4. The method according to claim 2,wherein in the setting step, the surface roughness of the impact area ofthe face portion is made smaller than the surface roughness outside theimpact area of the face portion.
 5. The method according to claim 1,wherein in the setting step, the surface roughness of the impact area ofthe face portion is set within a range of 1.0 μm (inclusive) to 4.0 μm(inclusive) as an arithmetic mean roughness.
 6. The method according toclaim 2, wherein in the setting step, the surface roughness of theimpact area of the face portion is set within a range of 1.0 μm(inclusive) to 4.0 μm (inclusive) as an arithmetic mean roughness. 7.The method according to claim 1, wherein the moment of inertia fallswithin a range of 2000 g·cm² (inclusive) to 6000 g·cm² (inclusive), andthe surface roughness outside the impact area falls within a range of2.0 μm (inclusive) to 8.0 μm (inclusive) as an arithmetic meanroughness.
 8. The method according to claim 2, wherein the bulge fallswithin a range of 200 mm (inclusive) to 600 mm (inclusive), and thesurface roughness outside the impact area falls within a range of 2.0 μm(inclusive) to 8.0 μm (inclusive) as an arithmetic mean roughness.
 9. Awood type golf club head including a face portion, a crown portion, anda sole portion, wherein the larger a moment of inertia of the golf clubhead is, the larger a surface roughness outside an impact area of theface portion is set, and the smaller the moment of inertia of the golfclub head is, the smaller the surface roughness outside the impact areaof the face portion is set.
 10. A wood type golf club head including aface portion, a crown portion, and a sole portion, wherein the larger abulge of the face portion is, the larger a surface roughness outside animpact area of the face portion is set, and the smaller the bulge of theface portion is, the smaller the surface roughness outside the impactarea of the face portion is set.